OLEDs and other electronic devices using desiccants

ABSTRACT

Electronic devices that use desiccants for protection from moisture. The electronic devices comprise a substrate ( 12 ) and an electronic organic element ( 22 ) disposed over the top surface of the substrate. The substrate has one or more voids ( 14 ) which store desiccants ( 24 ). The voids penetrate partially or completely through the thickness of the substrate. An environmental barrier ( 20 ) is disposed over the electronic organic element and the voids. Also provided are methods for making electronic devices that use desiccants.

RELATED APPLICATIONS

This application is a U.S. national stage application under 35 U.S.C.§371 of PCT/US2009/049691, filed Jul. 6, 2009, which claims priority toU.S. Provisional Application No. 61/078,633 filed 7 Jul. 2008, both ofwhich are expressly incorporated by reference thereto.

RESEARCH AGREEMENTS

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Princeton University, The University ofSouthern California, The University of Michigan and Universal DisplayCorporation. The agreement was in effect on and before the date theclaimed invention was made, and the claimed invention was made as aresult of activities undertaken within the scope of the agreement.

TECHNICAL FIELD

The present invention relates to protecting electronic devices, such asorganic light-emitting devices, from moisture by using desiccants.

BACKGROUND

Organic electronic devices, such as organic light-emitting devices(OLEDs), are susceptible to degradation when exposed to environmentalcontaminants, such as water vapor or oxygen. For example, exposure tomoisture and/or oxygen can cause degradation of the light-emittingmaterial, cause “dark spots” or pixel shrinkage, or reduce the usefullifetime of the OLED. To address this problem, OLED displays arecommonly fabricated on thick, rigid glass substrates with a glass ormetal cover sealed at the edges to enclose the light-emitting element.To provide further protection, it is conventional to also place adesiccant inside the sealed compartment enclosing the light-emittingelement. However, this desiccant arrangement is not suitable for manytypes of flexible OLEDs where a flexible thin-film barrier is used toencapsulate the device. Thus, there is a need for improved means toprotect electronic devices, such as OLEDs, from environmentalcontaminants.

SUMMARY

In one aspect, the present invention provides an electronic devicecomprising: a substrate having a void, wherein the substrate has a topsurface on one side and a bottom surface on the opposite side; adesiccant disposed in the void in the substrate; an organic elementdisposed over the top surface of the substrate; and an environmentalbarrier disposed over the organic element, wherein the environmentalbarrier covers over the void in the substrate.

In another aspect, the present invention provides a method for making anelectronic device, comprising: providing a substrate; creating a void inthe substrate; disposing a desiccant in the void; disposing an organicelement over the substrate; and disposing an environmental barrier overthe organic element and over the void in the substrate.

In another aspect, the present invention provides an electronic devicecomprising: a substrate having a void through the thickness of thesubstrate, the substrate having a top surface on one side and a bottomsurface on the opposite side; an organic element disposed over the topsurface of the substrate; an environmental barrier that conformallyencapsulates the organic element, wherein the environmental barrier isin contact with the substrate and seals over the void; an enclosedbottom chamber over the bottom surface of the substrate, the bottomchamber being in communication with the void; and a desiccant containedin the bottom chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show an OLED according to an embodiment of the presentinvention. FIG. 1A shows a cross-section side view of the OLED. FIG. 1Bshows a top view of the OLED.

FIG. 2 shows a cross-section side view of an OLED according to anotherembodiment.

FIG. 3 shows a cross-section side view of an OLED according to anotherembodiment.

FIG. 4 shows a cross-section side view of an OLED according to anotherembodiment.

FIG. 5 shows a cross-section side view of an OLED according to anotherembodiment.

FIG. 6 shows a cross-section side view of an OLED according to anotherembodiment.

FIG. 7A is a schematic illustration showing a cross-section side view ofa prototype that was constructed to demonstrate certain aspects of anembodiment of the invention. FIG. 7B shows photographs of the prototype,along with a comparative prototype, after 5 days of room air exposure.

DETAILED DESCRIPTION

The present invention provides electronic devices that use desiccantsfor protection from moisture. The electronic device comprises asubstrate and an organic element disposed over the top surface of thesubstrate. An environmental barrier is disposed over the organicelement.

Some of the characteristics of the substrate will vary depending uponthe particular application. Such characteristics include thetransparency (or opacity), flexibility (or rigidity), or permeability ofthe substrate. The substrate can be formed of any suitable materialknown to be used in substrates for electronic devices (e.g., metals,glass, polymers, semiconductors, ceramics, etc.), as selected accordingto the desired characteristics.

The organic element serves as the active portion (e.g., light-emittingor light-absorbing) of the electronic device. Such organic elements mayhave any of various architectures used for organic electronic devices.For example, many OLEDs are formed of a stack of organic films betweentwo electrodes.

The organic element is protected from environmental contaminants (e.g.,moisture and/or oxygen) by an environmental barrier that is disposedover the organic element. The environmental barrier may be any type ofstructure (e.g., covers, plates, films, layers, sheets, etc.) suitablefor protecting the electronic device from environmental contaminants.Some of the characteristics of the environmental barrier will varydepending upon the particular application. Such characteristics includethe transparency (or opacity), flexibility (or rigidity), or thicknessof the environmental barrier. These characteristics can be determined byvarious factors, including the material composition or dimensions (e.g.,thickness) of the environmental barrier.

The environmental barrier can be formed of any suitable material,including inorganic materials, such as metal oxides, metal nitrides,metal carbides, or metal oxynitrides. Other inorganic materials includesilicon oxides, silicon nitrides, silicon oxynitrides, aluminum oxides,indium-tin oxides, and zinc indium tin oxides. The environmental barriermay also be made of organic polymers such as parylene, polyesters,polyimides, polyethersulphones, etc. The environmental barrier may alsobe made of ceramics, including glasses such as borosilicate glass orsoda lime.

Where the environmental barrier is a rigid cover (e.g., glass), thecover may be adhered to the substrate by using any suitable adhesivematerial or other bonding technique. Where the environmental barrier isa thin film encapsulating the organic element, the film may be depositedby any suitable deposition technique, including physical vapordeposition, chemical vapor deposition, plasma-enhanced chemical vapordeposition, spin coating, etc. Such films may be single-layered ormulti-layered films. In some cases, the film may be any of the hybridlayers disclosed in U.S. Patent Application Publication No. 2008/0102223(for application Ser. No. 11/783,361 entitled “Hybrid Layers for Use inCoatings on Electronic Devices or Other Articles” filed on 9 Apr. 2007)or any of the multilayered coatings disclosed in U.S. Patent ApplicationPublication No. 2008/0102206 (for application Ser. No. 11/783,362entitled “Multilayered Coatings for Use on Electronic Devices or OtherArticles” filed 9 Apr. 2007), both of which are incorporated byreference herein in their entirety.

The substrate has one or more voids. In certain embodiments, desiccantsare stored in the void(s). By this arrangement, moisture that penetratesthrough or around the environmental barrier can be absorbed by thedesiccant contained in the voids. One of the problems with the use ofdesiccants in moisture-sensitive electronic devices is that thefootprint size of the devices may need to be increased in order toaccommodate the desiccants. Thus, storing the desiccant within thesubstrate in this manner can be useful in avoiding the need to increasethe footprint size of the device to accommodate the desiccants.

The voids can have any of various shapes or geometries, and as such, thevoids may be holes, openings, slots, grooves, channels, etchings, scribelines, perforations, pits, etc. The voids may penetrate partially orcompletely through the thickness of the substrate. The voids may becreated by any suitable excavation technique, including direct-writeetching using energetic beams (e.g., laser, ion, or electron),micromachining, microdrilling, or lithographic processes.

The voids are located at the periphery of the organic element. Further,the voids are covered by the environmental barrier. The shape of thevoids will vary depending upon the particular application (e.g., round,square, rectangular, etc). The size of the voids will vary dependingupon the particular application, and in some cases, the size of thevoids are in the range of 50 nm to 500 μm (as measured along its longestaxis).

In embodiments where the electronic device is an active-matrix OLEDhaving an array of the organic elements serving as active pixels, thevoids may be located at positions that substantially avoid obstructingthe transmission of light from the active pixels. For example, the voidsmay be located between the active pixels.

In certain embodiments, the voids may be openings through the fullthickness of the substrate. In some of such embodiments, the electronicdevice may further include a compartment on the bottom side of thesubstrate for containing additional desiccant. This compartment is incommunication with the openings, and thus, the additional desiccantprovides additional moisture-absorbing capacity. This feature may beuseful where the electronic device is a top-emitting OLEDs (where lightemission is primarily directed away from the substrate) because theadditional desiccant can be placed in the bottom compartment withoutconcern about obstructing the top-directed transmission of light fromthe light-emitting organic element. Thus, in addition to allowing forreduced footprint size (as mentioned above), the placement of desiccantsin this manner may further be useful in allowing greater desiccantcapacity without obstructing light transmission.

The material used for the desiccant can be any moisture-absorbingmaterial that is suitable for use in electronic devices, including theGroup 2A metals (e.g., calcium or barium) and their oxides (e.g.,calcium oxide or barium oxide).

In certain embodiments, the substrate and/or the environmental barrieris flexible. In such cases, lateral ingress of moisture through thesides of the electronic device can be a significant problem,particularly during flexion of the electronic device. As such, thisarrangement of the desiccant can be useful in impeding the lateralingress of moisture around the environmental barrier.

The electronic device may be any of various types of organic electronicdevices, including organic light-emitting devices, organic field-effecttransistors, organic photovoltaic cells, and organic photodetectors.Electronic devices fabricated in accordance with embodiments of theinvention may be incorporated into a wide variety of consumer products,including flat panel displays, computer monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18°-30° C., and more preferably at room temperature (20°-25° C.).

Referring to the embodiment shown in FIGS. 1A and 1B, a top-emittingOLED 10 comprises a metal foil substrate 12 having a plurality ofopenings 14 formed through the thickness of substrate 12. An organiclight-emitting element 22 is mounted on the top surface of substrate 12.Light-emitting element 22 comprises a stack of organic films between twoelectrodes (as conventional in many OLED architectures). Light-emittingelement 22 is covered with a transparent barrier film 20 that extendsover the edges of and encapsulates light-emitting element 22. Barrierfilm 20 is resistant to the penetration of environmental contaminants,and thereby, serves to protect light-emitting element 22. Barrier film20 also covers over openings 14.

FIG. 1B shows a top view of OLED 10 (barrier film 20 not shown). As seenin this view, light-emitting element 22 is surrounded on its peripheryby openings 14. Referring back to FIG. 1A, openings 14 are filled with adesiccant 24. Openings 14 may be created and/or filled with desiccant 24before or after light-emitting element 22 and/or barrier film 20 areprovided. By this arrangement, moisture that penetrates by lateralingress between barrier film 20 and substrate 12 can be absorbed bydesiccant 24 contained in openings 14.

OLED 10 further includes a bottom cover 16 on the bottom surface ofsubstrate 12. Bottom cover 16 creates a bottom compartment 18 on thebottom side of substrate 12 for containing additional desiccant 24.Because additional desiccant 24 is positioned on the bottom surface ofsubstrate 12, additional desiccant 24 can be provided withoutobstructing the outward transmission of light from light-emittingelement 22, and without needing to enlarge the footprint of OLED 10.Bottom cover 16 can be adapted to be opened or removable (e.g., usingmechanical means such as hinges, latches, screw on/off mechanisms, snapon/off mechanisms, etc.). This can allow for replacement of desiccant24.

Referring to the embodiment shown in FIG. 2, an OLED 30 (which can beeither top-emitting or bottom-emitting) comprises a polymer substrate 32having a plurality of openings 34 formed through the thickness ofsubstrate 32. An organic light-emitting element 42 is mounted on the topsurface of substrate 32. Light-emitting element 42 is covered with abarrier film 40 (which may be transparent if OLED 30 is top-emitting, ormay be opaque if OLED 30 is bottom-emitting) that extends over the edgesof and encapsulates light-emitting element 42. Barrier film 40 alsocovers over openings 34.

Because of its polymeric composition, polymer substrate 32 may bepermeable to environmental contaminants. To impede the passage ofenvironmental contaminants through substrate 32, the bottom surface ofsubstrate 32 is covered by another barrier film 36 (which may or may nothave the same composition as that of barrier film 40). By havingdesiccant 44 arranged in this manner, desiccant 44 can serve the dualfunction of impeding the lateral ingress of moisture at both the top andbottom surfaces of substrate 32. In an alternate embodiment, a barrierfilm also covers over the sides of the device such that the entiredevice is encapsulated by a barrier film (i.e., barrier film 40 andbarrier film 36 are continuous).

Referring to the embodiment shown in FIG. 3, a top-emitting OLED 50comprises a substrate 52 having a plurality of openings 54 formedthrough the thickness of substrate 52. An organic light-emitting element62 is mounted on the top surface of substrate 52. Openings 54 are filledwith a desiccant 64.

Light-emitting element 62 is covered by a transparent glass cover 60,which is sealed at its edges by a sealing adhesive 66 (e.g., aUV-curable liquid adhesive, such as epoxy resin) that bonds glass cover60 to substrate 52. Thus, light-emitting element 62 is enclosed in asealed chamber 68. By this arrangement of desiccant 64, moisture thatpenetrates into sealed chamber 68 can be absorbed by desiccant 64.

OLED 50 further includes a bottom cover 56 on the bottom surface ofsubstrate 52. Bottom cover 56 creates a bottom compartment 58 on thebottom side of substrate 52 for containing additional desiccant 64.Bottom cover 56 can be adapted to be opened or removable to allow forreplacement of desiccant 64.

Referring to the embodiment shown in FIG. 4, a top-emitting OLED 70comprises a substrate 72 having a plurality of openings 74 formedthrough the thickness of substrate 72. An organic light-emitting element82 is mounted on the top surface of substrate 72. Light-emitting element72 is covered with a transparent barrier film 88 that extends over theedges of and encapsulates light-emitting element 82. Barrier film 88 isresistant to the penetration of environmental contaminants, and thereby,serves to protect light-emitting element 82. Barrier film 88 also coversover openings 74. Further, barrier film 88 is provided with a hard,protective cover film 80, which is adhered to barrier film 88 by a layer86 of lamination adhesive.

Openings 74 are filled with a desiccant 84. By this arrangement ofdesiccant 84, moisture that penetrates by lateral ingress betweenbarrier film 88 and substrate 72 can be absorbed by desiccant 84contained in openings 74.

OLED 70 further includes a bottom cover 76 on the bottom surface ofsubstrate 72. Bottom cover 76 creates a bottom compartment 78 on thebottom side of substrate 72 for containing additional desiccant 84.Bottom cover 76 can be adapted to be opened or removable to allow forreplacement of desiccant 84.

Referring to the embodiment shown in FIG. 5, a bottom-emitting OLED 90comprises a polymer substrate 92 having a plurality of openings 94formed through the thickness of polymer substrate 92. An organiclight-emitting element 102 is mounted on the top surface of substrate92. To protect light-emitting element 102 from environmentalcontaminants, light-emitting element 102 is enclosed in a sealed chambercreated by a metal foil cover 100 that is provided over light-emittingelement 102 and sealed at the edges by a sealing adhesive 106 that bondsmetal foil cover 100 to substrate 92.

Since OLED 90 is a bottom-emitting OLED, polymer substrate 92 istransparent. However, the polymeric material in polymer substrate 92 canbecome a conduit for the diffusion of environmental contaminants throughsubstrate 92. To impede moisture penetration through the bottom side ofsubstrate 92, the bottom side of substrate 92 is covered with atransparent cover film 110 that serves as a barrier against moisture.Cover film 110 is bonded to the bottom of substrate 92 by adhesive bonds116.

However, even with these barriers, moisture may still have access routesthrough the sides or the top surface of substrate 92. To impede moisturepenetration through these routes, substrate 92 has a plurality ofopenings 94 which contain a desiccant 104. By this arrangement ofdesiccant 104, moisture that penetrates through substrate 92 can beabsorbed by desiccant 104.

Furthermore, a gap is maintained between bottom cover film 110 andsubstrate 92, such that any moisture that penetrates through cover film110 or laterally through adhesive bonds 116 can circulate within the gapand be absorbed by desiccant 104. Also, desiccant 104 is covered by acap 96 to contain desiccant 104 within openings 94.

In an alternate embodiment of OLED 90 in FIG. 5, metal foil cover 100and cap 96 may form a single unitary structure (which can eliminate theneed for sealing adhesive 106). Also, a barrier film, such as the oneused in OLED 30 of FIG. 2, may be used instead of cover film 110 (whichcan eliminate the need for adhesive bonds 116).

Referring to the embodiment shown in FIG. 6, a top-emitting OLED 120comprises a substrate 132 having a plurality of pits 124 that penetratepartially through the thickness of substrate 132. An organiclight-emitting element 122 is mounted on the top surface of substrate132. Pits 124 are filled with a desiccant 134. Pits 124 may be formedusing any suitable technique. For example, pits 124 may be formed bypartially excavating through substrate 132 (e.g., by laser ablation). Inanother example, pits 124 may be formed by making through-holes insubstrate 132, filling the through-holes with desiccant 134, and thenplugging the through-holes from the bottom side of substrate 132.

To protect light-emitting element 122 from environmental contaminants,light-emitting element 122 is covered with a barrier film 130 thatextends over the edges of and encapsulates light-emitting element 122.Barrier film 130 also covers over pits 124. By this arrangement ofdesiccant 134, moisture that penetrates by lateral ingress betweenbarrier film 130 and substrate 132 can be absorbed by desiccants 134contained in pits 124.

In another aspect, the present invention provides an electronic devicehaving a substrate with one or more voids (which may or may not befilled with a desiccant) extending through the thickness of thesubstrate. The organic element is disposed over the substrate andconformally encapsulated in an environmental barrier. The environmentalbarrier is also in contact with the substrate and directly on top of thevoid(s), i.e., it seals over the void(s). The device also has a bottomchamber beneath the substrate with the bottom chamber being incommunication with the void(s). The bottom chamber also contains adesiccant to absorb moisture that flows through the void(s) in thesubstrate.

FIG. 7A shows a prototype 150 that was constructed to demonstratecertain aspects of an embodiment of the invention. This prototype 150was made using a plastic substrate 152. In prototype 150, instead of anorganic element, a moisture detecting strip 154 was made on substrate152 by depositing a 100 nm film of calcium followed by a 5 nm film ofindium tin oxide (ITO). This moisture detecting strip 154 serves toindicate the amount of moisture to which an organic element in its placewould otherwise be exposed. A through-opening 178 was then cut throughplastic substrate 152 to allow the passage of moisture out through theback side of substrate 152. Moisture detecting strip 154 was thenencapsulated within a flexible 2 μm barrier film 156 as a moisturebarrier. Barrier film 156 had a hybrid silicon oxide/polymer compositionand was made in a manner described in U.S. Patent ApplicationPublication No. 2008/0102223 (for application Ser. No. 11/783,361 byWagner et al, filed 9 Apr. 2007). A hard protective coating 160 was thenapplied onto barrier film 156 via a laminating adhesive 162.

To form a bottom chamber 170, a cover glass 172 having a desiccant 174attached thereon was provided. Cover glass 172 was placed over the backside of substrate 152 and sealed with epoxy seals 168 to form bottomchamber 170. The inventors contemplate that the prototype shown in FIG.7A, with the calcium moisture detecting strip 154 being replaced by anorganic element, represents an embodiment of the present invention. Acomparative prototype was made in the same manner as above, except thatthe substrate did not have an opening.

FIG. 7B shows photographs of prototype 150 (upper panel) and thecomparative prototype (lower panel) after exposure to room air for 5days. As seen here, prototype 150 having the opening in the substratehas fewer defects in the calcium strip than the comparative prototypewithout the opening.

Despite the fact that the opening 178 is located away from the moisturedetecting strip 154 and completely sealed over by barrier film 156,prototype 150 demonstrated that substantial amounts of moisture thatwould otherwise contaminate the moisture detecting strip 154 is divertedthrough the opening 178. The inventors believe that this occurs becausemoisture penetration through barrier film 156 is primarily by lateraldiffusion through the film-substrate interface rather than through thebulk of barrier film 156. Thus, this embodiment may be particularlyuseful in electronic devices having barrier films in which interfacediffusion is the primary mode of moisture diffusion. Diffusion ofcontaminants into an electronic device can be measured using varioustechniques. For example, for organic light emitting devices, diffusioncan be measured using the technique described in Mandlik et al., AppliedPhysics Letters, vol. 93:203306 (2008).

In certain electronic device of the present invention, the diffusioncoefficient of atmospheric contaminants along the environmentalbarrier-substrate interface is greater than the diffusion coefficient ofatmospheric contaminants through the bulk of the environmental barrierwhen measured by accelerated storage testing (i.e., at atmosphericconditions of 1 atm, 65° C., and 85% relative humidity). In some cases,the interface diffusion coefficient is more than 4 orders of magnitudegreater than the bulk diffusion coefficient. As used herein,“atmospheric contaminants” means materials in the local atmosphere (suchas water or oxygen) that are detrimental to the performance of theorganic element.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. It is understood thatvarious theories as to why the invention works are not intended to belimiting.

What is claimed is:
 1. An electronic device comprising: a substratehaving an opening through a thickness of the substrate, wherein thesubstrate has a top surface on one side and a bottom surface on anopposite side; a desiccant disposed in the opening in the substrate; acover over the opening on the bottom surface of the substrate, whereinthe cover can be opened or is removable; an organic element disposedover the top surface of the substrate; and an environmental barrierdisposed over the organic element, wherein the environmental barriercovers over the opening in the substrate.
 2. The electronic device ofclaim 1, further comprising a bottom compartment located on the bottomsurface of the substrate, wherein the bottom compartment is incommunication with the opening, and wherein the bottom compartmentcontains additional desiccant.
 3. The electronic device of claim 1,wherein the environmental barrier is a flexible film encapsulating theorganic element.
 4. The electronic device of claim 1, wherein theopening is located at a periphery of the organic element.
 5. Theelectronic device of claim 1, wherein the electronic device is anorganic light-emitting device comprising an array of organic elementsthat serve as active pixels, wherein the opening is located at aposition to substantially avoid obstructing the transmission of lightfrom the active pixels, and wherein the opening is located between theactive pixels.
 6. The electronic device of claim 1, wherein theelectronic device is a top-emitting organic light-emitting device. 7.The electronic device of claim 1, wherein the electronic device is abottom-emitting organic light-emitting device.
 8. The electronic deviceof claim 1, wherein the substrate is formed of a metallic material. 9.The electronic device of claim 1, wherein the substrate is formed of apolymeric material.
 10. The electronic device of claim 1, wherein, thesubstrate is flexible.
 11. The electronic device of claim 1, furthercomprising a bottom environmental barrier disposed over the bottomsurface of the substrate, and wherein a composition of the bottomenvironmental barrier is the same as or different from the environmentalbarrier that is disposed over the organic element.
 12. The electronicdevice of claim 1, wherein the device is made by steps comprising:creating a through-hole in the substrate; filling the through-hole withthe desiccant; and plugging a bottom side of the through-hole.
 13. Theelectronic device of claim 1, wherein the environmental barrier is arigid cover that is attached to the substrate to form a sealed chambercontaining the organic element.